This invention relates in general to prefabricated buildings and, more particularly, to a building that utilizes preferably prefabricated, cold formed steel wall panels and prefabricated, hollow core concrete floor slabs. When completed, the prefabricated walls and floor slabs provide a structural support system for the building. The invention also relates to a method for fabricating and erecting such a support system.
In low rise multi-story buildings having steel structural support systems, prefabricated light weight steel framing (L.W.S.F.) is predominantly used. The basic building component of light weight steel framed structures is the cold formed shape. The use of light weight steel framing was heavily influenced by wood framing. The "2 by" member, e.g., "2.times.4", of wood framing was simply replaced with a cold formed "C" or "Z" shaped, thin steel section. In building design, prefabricated, light weight steel framed wall panels are divided essentially into two categories: (1) curtain wall and (2) load bearing. Curtain wall studs are flexural members used in non-bearing, exterior wall panels that are designed to resist only wind loads, axial loads due to the weight of the curtain wall itself and the weight of finishes only. These members provide structural support for a variety of exterior finishes including masonry veneer, stucco, synthetic veneers and exterior insulation with finish systems.
Interior finishes such as gypsum wall board may be attached directly to the light weight steel framing. A typical stud wall is arranged between floor slabs. The bottom of each wall stud is located in a bottom track while the top of the stud is located in an inner track, which is received within an outer top track. The tracks are typically connected to the floor slabs by drilled expansion anchors.
A total load bearing system constructed from light weight steel framing includes studs and planks. A load bearing stud is designed to support axial and wind loads while a joist is designed to support the interior dead load and live load of the building. A known type of construction for a light weight steel framed building is comprised of axial load bearing studs, joists, and rafters for platform type construction. In platform type construction each floor acts as a working platform for the construction of the next story. Axial load bearing studs are located between the top and bottom tracks. Concrete stops or subfloor edge supports are arranged at the inner side of the bottom tracks for defining the ends of a floor, which may be constructed from plywood or poured concrete. Studs have "C" shaped cross sections defined by a web, two flanges connected to the ends of the web and lips connected to the free ends of the flanges to stiffen the flanges.
In low rise concrete buildings, the hollow core slab system of construction has been used. The basic component of the hollow core slab system of construction is a prefabricated, prestressed concrete member or slab having a series of continuous voids. The slabs may be arranged to form walls, floors, roof decks and spandrel panels. Hollow core slabs are most widely known for providing economical floor and roof systems. The most common use of hollow core slab is found in "block and plank" structures where the prefabricated, hollow core slabs form the floors and roof, which are supported by concrete block walls. Finishes may be applied directly to the top and/or underside surface of the hollow core slabs.
The continually rising cost of building construction and the longstanding need for affordable housing have motivated the building design community to consider alternative construction materials and methods of constructing low rise multi-story buildings. In the past, the use of a steel structures or concrete structures, such as those described above, have dominated the building industry.
Parent application Ser. No. 07/999,431 solves many of the problems associated with these prior structural support systems to significantly reduce construction costs and satisfy the need for affordable housing. This is accomplished by combining the most cost effective component of the prefabricated, steel stud building system with the most cost effective component of the prefabricated, concrete system to provide a unique structural support system. The stud is the most efficient component of the light weight steel framing system because it is a stiffened channel that has tremendous axial load capabilities for its relatively light weight. The plank or slab is the most efficient component of the hollow core slab system because the prestressed concrete plank provides efficient load carrying capacity and deflection control, particularly when used for floor and roof systems.
The parent application describes a structural system for supporting a building having a first level of preferably prefabricated, light weight steel framed, bearing wall panels, each having a bottom end attached to a foundation and a top end for supporting a floor, in which the bearing wall panels are spaced at predetermined intervals in a first direction along the foundation. A first level of prefabricated, hollow core concrete floor slabs having longitudinal sides and transverse ends is positioned upon the top ends of adjacent bearing wall panels such that the longitudinal sides of longitudinally adjacent slabs form keyways extending parallel to the first direction and the transverse ends of transversely adjacent slabs form butt joints extending perpendicular to the keyways. A plurality of connection members positively interlock the bearing walls to the slabs thereby forming a unitary structure in which the floor slabs and bearing walls are interlocked.
In particular, the parent application provides for splice plates attached to the top ends of the wall having at least one hole aligned with a respective keyway. Each keyway includes at least one first reinforcing bar received in the aligned hole of the splice plate and each butt joint may include at least one second reinforcing bar extending parallel to the butt joint. The keyways and butt joints are filled with grout. Each splice plate may include a number of holes that automatically accommodate for tolerances during construction. A similar type of connection may be provided at the exterior bearing wall to floor slab connections.
A first set of preferably prefabricated, exterior non-bearing wall panels may be attached to the foundation and to the first level of floor slabs in a position perpendicular to the bearing wall panels, while a second set of exterior non-bearirig walls may be attached to the foundation and to the exterior bearing walls in a position parallel to bearing wall panels. The first set of exterior non-bearing walls may be attached after installation of the first level of bearing wall panels and floor slabs or after additional stories are installed. The second set of exterior non-bearing walls also may be attached after installation of the first level of bearing walls and floor slabs or after additional stories are installed. Alternatively, the second set of exterior non-bearing walls may be attached to the exterior bearing wall panels during prefabrication.
When multi-story buildings are being constructed, a second level of preferably prefabricated, bearing wall panels is attached to the first level of floor slabs such that the second level studs are in vertical alignment with the first level studs of bearing wall panels below. A second level of floor slabs then is positively interlocked with the second level bearing walls in the same manner as first level panels discussed above. Shims may be inserted between the first level of floor slabs and the bottom end of the second level bearing wall panels to eliminate any spacing therebetween to provide for full bearing connections.
The structural support system of the parent application also provides a unique connection between cross bracing at the bearing wall to floor slab intersections. The cross bracing is formed from flat straps, diagonally attached to each side of a predetermined number of bearing walls in an "X" shape during prefabrication of the wall panels. The bottom of the first level of cross bracing is attached to the foundation. Wind posts, which may be formed as double stud combinations in the bearing wall, are provided at all post locations of the cross bracing. Wind posts of the second level bearing walls provided with cross bracing are in vertical alignment with the wind posts of the first level, cross braced, bearing wall panels. The vertically aligned wind posts of each level are directly connected to each other for transferring loads. The connection may be formed by at least one vertical, threaded rod and bolt provided in the butt joint between transverse ends of adjacent slabs. The threaded rods may be connected between the wind posts by bearing angles attached to the wind posts.
The parent application also includes improvements in the light weight steel framed bearing wall panels used in the invention, but which may be employed in other types of support systems, as well. By grinding the edges of the bearing plates, which are placed between the ends of the load bearing studs and the cold formed, continuous steel tracks of the bearing wall panels, the beating plates lie flush against the web of the track. Without grinding, the plates are spaced from the web of the track by the curved comers of the tracks, which are formed during the cold forming process. With the bearing plates lying flush against the web, the full beating capacity of the plate may be employed, thereby enabling a decrease in the amount of steel required in the support system without decreasing the load-carrying capacity of the wall.
The positive connection between bearing wall panels and floor slabs is made by welding or mechanically fastening a bearing plate to the top of the bearing walls and then welding or fastening the bearing plate to embedded plates provided in the floor slabs. The floor slabs rest upon the overhanging outer portions of the bearing plate and the upper level wall is connected directly to the bearing plate. Alternatively, the bearing wall-floor slab connection is made by cutting grooves in the top surface of the floor slabs. The grooves extend parallel to the butt joints and communicate with the butt joints such that poured grout fills the grooves and butt joints to form a level surface upon which the upper level wall is connected. Altematively, the bearing wall-floor slab connection is made by welding or mechanically fastening embedded plates provided in the floor slabs directly to the top track of the bearing wall.
While the structures taught in the parent application indeed provide many advantages, several important improvements have recently been devised.